Was/Were in the past
Ok so I was studying an article yesterday of which I had both the English and Spanish translations and thought that I would pay special attention to where the words 'was' or 'were' were used to help me really get my head around the ser/estar pret/imp choice.
I had actually thought that I was getting it and I know that I do tend to overthink things sometimes which may be exactly what I'm doing here but I'm posting my musings partly to clarify things in my mind and in case someone out there is at the same level and might find the following interesting if not helpful.
Btw here's an article that others may find useful: Past tenses of ser and estar
But back to the article that I was studying, firstly I was surprised how infrequently the English word 'was' was translated by ser or estar in a past tense etc and instead the imperfect or preterite form of the actual verb was used: (although I have to say the opposite also occurred in some instances)
eg
Eng version - how much longer was that day of rest to continue?
Spanish version - ¿hasta cuándo duraría el día de descanso?
English version - the purpose was clearly explained
Spanish version - les explicó claramente su propósito.
But here are some examples where ser or estar were used along with my thoughts as to why, I would greatly appreciate any one else's take on the matter: Some seem fairly straightforward and others have me fairly bamboozled 
Eng - they were the chosen people
Spanish - era el pueblo elegido
Why? Ser = CID, imp = because it 'was' over an indefinite period of time and was not an action
Eng - it was a great honor
Spanish - era un honor inmenso
Why? Same dealio - what kind of honor was it? CID = Ser, imp because it 'was' that way over an indef' period and it wasn't an action.
Now this one was a bit trickier:
The English was quite different as the being blind bit was figurative so the English version used the word 'shortsighted':
Eng - How fleshly, how shortsighted - they were!
Spanish ..... demonstraba lo ciegos que estaban y lo egoístas que eran.
I'm not sure why 'lo' was used there in place of 'que' - any ideas?
Why? So I'm guessing that because it was figurative instead of literal blindness estar is the verb of choice and once again over an indef' period instead of a sudden action it would have to be the imperfect. But then with egoístas that would have been a personality trait so ser for CID.
Eng: ... preferring instead the leeks.
Spanish: ...lo único que les importaba eran los puerros.
Why? Once again not a word for word translation and this is one where I probably would have vacilated between eran and fueron so I'm thinking that I have to consider the preterite more for actions and the imp for descriptions, would that be fair? Ser = identifying.
Eng: Like ungrateful Esau....
Spanish: Fueron tan ingratos como Esau quién no dudó en ....
Why? Ok so based on the previous example I'm guessing that the preterite was used here because the author had in mind one particular action of Esau's? I wonder why though ser was used - wouldn't ungrateful be similar to shortsighted or could it have gone either way with ser or estar and for that matter with the pret or imp? Any input on this one gratefully received
Eng: They were more obedient than their fathers had been.
Spanish: Fueron más obedientes que sus antecesores.
Why? Ok this really highlights the problem that I have with these two verbs in the past - more obedient surely that's a classification - happened over an indefinite period of time, why not eran? Now this bit was referring to 'la siguiente generación' is that enough to encapsulate it down to a specific time period therefore necesitating the preterite? ay ay ay - someone please put me out of my misery and tell me that you've figured this business out lol.
But if that's the case - why do we next have ¿Cuál era el problema?
Surely if it's just one problem that's narrowed down to a particular time or ocurrence - why not the preterite there?
Same with - ya no era possible .....
Ok I'm going to leave it there for now - estoy pendiente de ustedes!
9 Answers
Eng - How fleshly, how shortsighted - they were!
Spanish ..... demonstraba lo ciegos que estaban y lo egoístas que eran.
I'm not sure why 'lo' was used there in place of 'que' - any ideas?
Lo + adjective + que is another use of the neuter lo article, and in this case it translates as how + adjective. This use of lo is special since it can take adjectives of any number (singular or plural) and/or gender (masculine or feminine).
¡Ni idea tienes de lo buenas que son! = You have no idea how good they are! (pertaining to things/people that are feminine in gender)
Si solo supieras lo agradecida que estoy.. = If you only knew how grateful I am (singular female subject)..
P.S.: This phrase means the same as "qué (w/ accent) + adjectivo" and "cuán + adjetivo" (but not in exclamatory sentences; for "She's so beautiful!" you say "¡Qué guapa es!" but you cannot say "¡Lo guapa que es!").
"los ciegos" = noun [the blind (people)]
"los egoístas" = noun [the selfish (people)]
Also:
los ricos = noun (the rich)
los pobres = noun (the poor)
But:
lo ciegos (que) = adverb (how blind) (plural, masculine)
lo egoístas (que) = adverb (how selfish) (plural, masculine/feminine)
Notes:
1) Lo is a neuter article, that's why it doesn't conform to the subject's gender nor to its number.
2) I could be wrong in labeling the second set as adverbs. The point is that if you also pluralize the (neuter) article, you'd come up not with a "how + adjective" phrase but with a noun.
Ok I'm thinking about the ¿cuál era el problema? I think it's the question form that's putting me off but really, even though it's in a question form, it's still a description isn't it?
It's just that as a statement it's easier to see (probably just for my weird mind) - ie. El problema era ..... so identifying the problem that wasn't an action but remained over an indefinite period of time ser & imp. Good, think I've got that.
and the 'ya no era possible' is the same, I think it's the negative form that's putting me off but that too is still a description that CID's what ever it was as in the 'not possible' category lol 
what was it? or rather what wasn't it? it wasn't possible and it would have stayed that way = ser/imp
Kiwi, as you well know, I am a minus 101 beginner!!
However, Russian is even more difficult when it comes to the "preterite or imperfect" choice.
So I have two observations -- which may be entirely useless:
(1) I notice that you did not include the whole sentence/phrase in some cases.
For example,
Like ungrateful Esau....
Now, if the reference were actually to an event, then we know we use ser with the location of events and estar with the location of inanimate and animate objects. Could the author have had in mind the location, i.e., the Biblical event? I know it's a stretch, but sometimes my biggest mistake is confusing the location of event verses object.
(2) If I learned anything from my hair loss with the preterite or imperfect question in Russian it was
neither are correct and both are correct
The real question, as Patch pointed out, is what the speaker believes the most important to communicate. I.e., "there was no end to the trouble with this child during the year he/she stayed with us" verses "the only trouble we had with this child was the one isolated event I am describing."
I the speaker choose, at the time of utterance, which verb best communicates my thought. So if the cause is more important to me than the result, I might choose my verb accordingly.
For example, I might use the imperative for focusing the listener on the cause for a particular state, rather than the length of time something(s) remained in the state.
Or, if the result of the action taken is what is important to me, I might use the preterite to focus the attention on the fact the event ended in a particular state.
In effect, I choose which verb to use, depending on where I want your attention directed.
Sure hope this long rambling helped in some way. Basically, what I am saying is you may want to try making up sentences choosing either ser or estar and see if that helps bring it closer to an "ingrained response." 
That's a lot of questions KG! If we're talking about that "imperfect" vs. preterite" thingy ie...
el problema era vs. el problema fue
I interpret the second one as "The problem was [something] and then stopped being a problem. The first I interpret as "The problem was [something] ... and probably continued to be ... I think it comes back to that "rule" about something being finished or ongoing in the past. Another example -
Quise un helado (the "wanting" has finished in the past - I got the ice cream so the "wanting" is gone)
Quería un helado (I have not told you that the wanting has gone so I probably didn't get it. I might even still be wanting it)
Was this what you had in mind or something different?
This insight was given by Geouk on another thread but I thought it might be helpful to add it here as well - of course if Geouk stops by and wants to add anything else that would be fabulous 
Let's try to shed some light over the use of 'estaba' and 'estuve'. It is a tricky one though, so down to semantics, without being too technical, it works like this:
Estaba... related to the circumstances the person was in. e.g. "Estaba (él/ella) cocinando cuando sonó el teléfono", "She was cooking when the phone rang".
Estuve...related to a continuous action that ended at some point. "Estuvo (él/ella) cocinando toda la mañana y luego salió", "She cooked all morning and then she left".
@ Webdunce
You might find this reference useful:
Lo may also be used adverbially before an adjective that shows agreement with a noun, being equivalent to the relative adverb 'how', as in lo buenas que son 'how good they (f.pl.) are' (Butt & Benjamin (2004),
Spanish ..... demonstraba lo ciegos que estaban y lo egoístas que eran.
Using lo + a plural adjective is throwing me for a loop. I did not know that was possible. :(
I would have said "los ciegos que" and "los egoístas que" (not that I would have been correct).
Also, were I to refer to a group of blind females (figuratively or literally), I would say "las ciegas que" (again, don't know if that's right...it's just what I would do currently).
This whole article + adjective + que for how + adjective is something I have not encountered before.
Any other thoughts?
